This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 11-365755 filed on Dec. 24, 1999, the entire content of which is incorporated herein by reference.
This invention generally relates to vehicle engines. More particularly, the present invention pertains to a variable valve timing system for controlling the opening and closing timing of an intake valve and an exhaust valve of a vehicle engine while the engine is actuated or operating.
Known variable valve timing systems are described in Japanese Patent Laid-Open Publication H01-92504 and Japanese Patent Laid-Open Publication H09-250310. The disclosed variable valve timing systems include a rotation transmitting member rotatably supported in a predetermined range relative to a rotation member rotating with a cam shaft. The rotation transmitting member transmits a rotation force from a crank sprocket or a pulley of a crankshaft, and is provided with a recessed portion at its inner peripheral portion. The variable valve timing system also includes a plurality of vanes provided on the rotation member, a fluid pressure chamber formed between the recess portion and the rotation member and divided into an advanced angle chamber and a retarded angle chamber by the vane, a first fluid conduit supplying fluid to and discharging the fluid from the advanced angle chamber, a second fluid conduit supplying fluid to and discharging the fluid from the retarded angle chamber, and a relative phase restricting mechanism restricting a relative phase between the rotation member and the rotation transmitting member when the relative phase between the rotation member and the rotation transmitting member corresponds to the predetermined phase.
In the variable valve timing system disclosed in the publications mentioned above, the rotation member is rotated relative to the rotation transmitting member to move the vanes in the advanced angle direction of the recess portion to a certain position until reaching the most advanced angle position to advance the angle of the valve opening and closing timing by supplying the operation fluid to the advanced angle chamber via the first fluid conduit and discharging the operation fluid from the retarded angle chamber via the second fluid conduit. The rotation member is rotated relative to the rotation transmitting member to move the vane of the recess portion in the retarded angle direction to a certain position until reaching the most retarded angle position to retard the angle of the valve opening and closing timing by supplying operation fluid to the retarded angle chamber via the second fluid conduit and by discharging the operation fluid from the advanced angle chamber via the first fluid conduit.
With further regard to the variable valve timing system disclosed in the publications mentioned above, the rotation member is always affected by the force in the retarded angle direction by a variable torque affecting the cam shaft during the engine operation. When the supply of operation fluid to the fluid pressure chamber stops as the engine stops, the vane is not able to be locked by the fluid pressure of the fluid pressure chamber, the rotation member is rotated in the retarded angle direction relative to the rotation transmitting member (until the crankshaft is completely stopped) to stop the rotation member and the rotation transmitting member at the relative phase in accordance with the relative phase therebetween immediately before the engine stops. When the engine is started in this condition, the rotation member is rotated in the retarded angle direction relative to the rotation transmitting member by the fluid pressure in the retarded angle direction and the vane reaches the phase at the most retarded angle position where the vane contacts the peripheral direction end surface of the advanced angle side of the recess portion. When the engine is started in this condition, the vane stays unstable until the fluid pressure in the fluid pressure chamber is increased to lock the vane, and the vane is vibrated by the variable torque affecting the cam shaft to contact a peripheral end surface of the recess portion and thus generates noise. To avoid this drawback, the relative phase between the rotation member and the rotation transmitting member is restricted at the most retarded angle position by the relative phase restricting mechanism.
In general, the volumetric efficiency is improved by delaying the closing timing of the intake valve to improve the output of the engine because the intake air enters the cylinder by inertia even after the piston starts to move towards the top dead center at the high speed velocity area of the engine.
However, in the case of the variable valve timing systems disclosed in the aforementioned publications for controlling the opening and closing timing of the intake valve, because the valve timing for opening and closing at the most retarded angle position is required to be determined at the time when the air can be taken in at the start of the engine, it is difficult to improve the volumetric efficiency by retarding the closing timing of the intake valve to utilize the inertia of the intake air at the high speed velocity area. When the valve opening and closing timing at the most retarded angle position is determined at the time capable of improving the volumetric efficiency by the inertia of the intake air, the intake valve is opened even after the piston passes the bottom dead center position and moves towards the top dead center position at the engine start at the most retarded angle position. Moreover, because the intake air is not accompanied by inertia, once sucked or drawn-in intake air is reversely moved to be discharged not to raise the compression ratio to generate the condition which cannot achieve the combustion. This may cause difficulty with respect to the engine start. This problem tends to be generated at the place with low pressure when the closing timing of the intake valve is determined after the piston passes the bottom dead center position even when the valve opening and closing timing at the most retarded angle position is determined at the time capable of taking in the air at the engine start and even when the valve opening and closing timing at the most retarded angle position is not determined at the time capable of improving the volumetric efficiency by the inertia of the intake air.
When the variable valve timing system in the aforementioned publications is used for controlling the opening and closing of the exhaust valve, the retarded closing timing of the exhaust valve elongates or extends the overlapping period of the intake valve and the exhaust valve, thus deteriorating the engine start by increasing the internal EGR volume (exhaust gas re-circulation volume).
To address the aforementioned problems, Japanese Patent Laid-Open Publication H09-324613 describes a system in which the relative phase between the rotation member and the rotation transmitting member is restricted by the relative phase restricting mechanism at a middle position moved to the advanced angle by a predetermined angle compared to the most retarded angle position in accordance with the valve opening and closing timing capable of improving the volumetric efficiency by the inertia of the intake air. However, in this system, it is only for a brief moment that the relative phase of the rotation member and the rotation transmitting member is positioned at the predetermined middle position when the rotation member rotates in the retarded angle direction relative to the rotation transmitting member at the engine stop. Accordingly, the relative phase between the rotation member and the rotation transmitting member cannot be completely restricted at the predetermined middle position by the relative phase restricting mechanism and noise may be generated by contact between the vane and the peripheral end surface of the recess portion of the rotation transmitting member at the engine start, and so smooth start of the engine cannot be achieved.
In light of the foregoing, a need exists for a variable valve timing system which can improve smooth engine start while also preventing noise generation by the vane during engine start.
A need also exists for a variable valve timing system that is capable of enlarging the variable timing control area.
In light of the foregoing, the present invention provides a variable valve timing system that includes a rotation member rotating with one of a crankshaft and a cam shaft, a rotation transmitting member rotatably supported on the rotation member relative to the rotation member within a predetermined range and rotating with the other of the crankshaft and the cam shaft, a vane provided on the rotation member, and a fluid pressure chamber formed between the rotation member and the rotation transmitting member and divided into an advanced angle chamber and a retarded angle chamber by the vane. The rotation member and the rotation transmitting member are relatively rotated by the fluid pressure applied to the advanced angle chamber and the retarded angle chamber, and the opening and closing timing of the valve actuated by the camshaft is varied by changing the rotation phase of the cam shaft relative to the rotation phase of the crankshaft. The variable valve timing system also includes a first relative rotation restricting mechanism that restricts relative rotation between the rotation member and the rotation transmitting member from the most advanced angle position where the volume of the retarded angle chamber is the minimum to the most retarded angle position where the volume of the advanced angle chamber is the minimum at the position corresponding to the engine start at which the vane is positioned approximately in the middle of the fluid pressure chamber and releases the restriction by the fluid pressure towards the retarded angle chamber. A second relative rotation restricting mechanism restricts the relative rotation of the rotation member and the rotation transmitting member from the most retarded angle position to the most advanced angle position at the position corresponding to the engine start and releases the restriction by fluid pressure towards the advanced angle chamber.
Although the vane cannot be locked by the fluid pressure of the fluid pressure chamber to rotate the rotation member in the retarded direction relative to the rotation transmitting member when the supply of operation fluid to the fluid pressure chamber is stopped at the engine stop, the relative phase between the rotation member and the rotation transmitting member is locked at the position corresponding to the engine start, where the vane is positioned approximately in the middle of the fluid pressure chamber by the first relative rotation restricting mechanism and the second relative rotation restricting mechanism at the engine start. Consequently, the noise which might otherwise be generated by the contact between the vane and the peripheral end surface of the fluid pressure chamber at the engine start can be inhibited or substantially prevented.
Because the valve opening and closing timing at the engine start is obtained at the relative phase of the rotation member and the rotation transmitting member when the vane is positioned at the engine start position, at the most retarded angle position the opening and closing timing of the vane can be further retarded compared to the relative phase at the position corresponding to the engine start. Accordingly, an improvement in the volumetric efficiency can be realized by utilizing the inertia of the intake air, and the valve opening and closing timing at the engine start can be advanced to achieve smooth starting of the engine by not generating compression ratio deterioration.
The first relative rotation restricting mechanism may include a first restricting member biased by a spring and accommodated in either one of the rotation member and the rotation transmitting member, and a first restricting groove formed either on the rotation member or the rotation transmitting member to allow relative rotation between the rotation member and the rotation transmitting member from the position corresponding to the engine start to the most advanced angle position by the positioning the first restricting member in the first restricting groove, and to restrict relative rotation from the position corresponding to the engine start to the most retarded angle position. The second relative rotation restricting mechanism may include a second restricting member biased by spring and accommodated in either the rotation member or the rotation transmitting member and a second restricting groove formed either on the rotation member or the rotation transmitting member to restrict the relative rotation of the rotation member and the rotation restricting member from the position corresponding to the engine start to the most advanced angle position by positioning of the second restricting member in the second restricting groove, and to allow relative rotation from the position corresponding to the engine start to the most retarded angle position.
In the variable valve timing system of the present invention, a biasing member is provided to apply a predetermined biasing force that always biases the rotation member towards the advanced angle side relative to the rotation transmitting member.
According to another aspect of the invention, a variable valve timing system for an internal combustion engine includes a rotation member rotating with either a crankshaft or a cam shaft, a rotation transmitting member rotatably supported relative to the rotation member within a predetermined range and rotating with the other of the crankshaft and the cam shaft, a vane provided on the rotation member, and a fluid pressure chamber formed between the rotation member and the rotation transmitting member and divided by the vane into an advanced angle chamber and a retarded angle chamber. The rotation member and the rotation transmitting member are relatively rotated by fluid pressure in the advanced angle chamber and the retarded angle chamber, with a rotation phase of the cam shaft changing relative to the rotation phase of the crankshaft to change opening and closing timing of a valve. A first relative rotation restricting member restricts relative rotation between the rotation member and the rotation transmitting member from a most advanced angle position in which the volume of the retarded angle chamber is a minimum to a most retarded angle position in which the volume of the advanced angle chamber is a minimum at a position corresponding to the engine start at which the vane is positioned at approximately a middle of the fluid pressure chamber and releasing a first restriction by the fluid pressure greater than a first predetermined pressure after the engine start. A second relative rotation restricting member restricts relative rotation between the rotation member and the rotation transmitting member from the most retarded angle position to the most advanced angle position and releases a second restriction by the fluid pressure at greater than a second predetermined pressure after the engine start.
Another aspect of the invention involves a variable valve timing system for an internal combustion engine that includes a rotation member adapted to rotate together with either a crankshaft or a cam shaft, a rotation transmitting member supported with respect to the rotation member for relative rotation between the rotation member and the rotation transmitting member within a predetermined range, a vane provided on the rotation member, and a fluid pressure chamber formed between the rotation member and the rotation transmitting member and divided by the vane into an advanced angle chamber and a retarded angle chamber. The rotation member and the rotation transmitting member are relatively rotated by fluid pressure applied to the advanced angle chamber and the retarded angle chamber to change the opening and closing timing of a valve to be actuated by the cam shaft by changing the rotation phase of the cam shaft relative to the rotation phase of the crankshaft. The system also includes a first bore provided in either the rotation member or the rotation transmitting member, a first groove provided in the other of the rotation member and the rotation transmitting member, and a first pin slidably received in the first bore for sliding movement between one position in which a portion of the first pin is received in the first groove to restrict relative rotation between the rotation member and the rotation transmitting member to an engine start position at which the vane is positioned at approximately a middle of the fluid pressure chamber and a second position at which the portion of the first pin is moved out of the first groove by fluid pressure to restrict relative rotation between the rotation member and the rotation transmitting member from a most advanced angle position in which a volume of the retarded angle chamber is a minimum to the engine start position.